This invention relates to a retractable suspension for the wheels of a vehicle and in particular to a vehicle having a retractable suspension.
The invention will be described by way of example with reference to the vehicle being a towable vehicle such as a trailer or the like. It should be understood that this is by way of example only and that the invention is not limited to such vehicles.
Known trailers typically have a chassis terminating at a drawbar assembly or the like at one end thereof, a body mounted on the chassis and wheels secured to the chassis via suspension components. The body has a load receiving surface or bed and in use, that bed, when the drawbar assembly is secured to a towing vehicle, is spaced from the ground by a predetermined distance.
It is often difficult to load such a trailer because the bed is above ground level.
Numerous earlier proposals have been suggested for providing a trailer or vehicle with a bed which can be moved relative to the ground such that the bed may be moved between a raised towing position and a lowered loading position. With such proposals the disadvantage referred to above existing in known trailers was eliminated.
U.S. patent specification 2,230,014 discloses a trailer having a bed which could be raised or lowered with respect to the ground. The trailer had a generally U-shaped chassis when viewed in plan and the bed was coupled thereto by two boomerang shaped linkages. These linkages occur at longitudinally spaced positions along the chassis and are linked so that both of them could be moved by an hydraulic cylinder to raise and lower the bed. U.S. Pat. No. 2,934,228 and 3,468,440 disclose similar arrangements.
The difficulty with such earlier proposals was that they could not be readily adapted for vehicles other that trailers. In addition, the arrangements tended to be complex in construction.
U.K. patent specification 1,124,791 disclosed a retractable suspension for the wheels of a vehicle and in particular for towable vehicles such as trailers. This specification disclosed a trailer having tandem pairs of wheels. Each wheel was mounted to a free end of a wheel arm and the other end of the wheel arm was pivotally mounted to the vehicle chassis. A damper or suspension cylinder extended between that part of the arm to which the wheel is mounted and a lever. One end of the lever was pivotally mounted to the chassis adjacent the mount for the wheel arm and the other end of the lever had an hydraulic cylinder coupled to it. The cylinder joins the levers associated with a pair of wheels and extension of the cylinder caused the wheel arms to pivot to enable the bed of the vehicle to be lowered relative to the ground.
This U.K. specification disclosed a second embodiment where the lever referred to above was replaced by a leaf spring assembly. In both embodiments, one of the wheel arms formed a leading wheel arm and the other a trailing wheel arm.
Because the wheel arms were trailing and leading wheel arms the arrangement of the U.K. patent specification could not readily be adapted to operate with a vehicle having three pairs of wheels. In addition, the arrangement was such that extension of the cylinder caused the bed of the vehicle to move relative to the ground under the influence of gravity. Retraction of the cylinder effected lowering of the suspension and hence raising of the vehicle bed. During raising and lowering the wheel arms and levers were relatively unsupported.
It is an object of the present invention to at least minimise the disadvantages referred to above.